The present invention relates to polyamide pre-polymers, polyamide polymers, a process for producing polyamide pre-polymers and polyamide polymers, and the resins resulting from reacting a polyamide polymer with an epihalohydrin. The resins of the present invention may be used as wet strength resins and/or creping aids in the papermaking industry as well as surface additives for wool.
In the paper industry, poly(aminoamides) made from adipate and diethylenetriamine (DETA) are commonly used as pre-polymers for the preparation of polyamide polymers, and ultimately, wet strength resins (e.g. H. H. Espy, TAPPI J., 78, 90 (1995)). Typically, to result in a resin, a polyamide polymer is treated with epichlorohydrin, which reacts with the secondary amine on the polyamide polymer backbone to form azetidinium, chlorohydrin, epoxide or other functionalities necessary for self-crosslinking and reacting with the pulp fiber. Despite the use of this polymer, other poly(aminoamides) with novel structures are still being sought.
U.S. Pat. No. 3,159,612 (Tsou et al. ""612), U.S. Pat. No. 3,305,493 (Emmons), and British Patent 1,051,579 (Tsou et al. ""579) describe the synthesis of alternative polyamide polymers; however, each teaches a process where different polymer structures and different molecular weights than those contemplated by the present invention are obtained. More particularly, Tsou et al. use a one-step reaction process, involving a diamine and an acrylic or methacrylic ester. Emmons describes a process having xe2x80x9ctwo stepsxe2x80x9d, however both reactants (a diamine and an acrylic or methacrylic ester in a 1:1 molar ratio) are added all at once. Thus, except possibly with respect to the reaction temperature (in the case of acrylic ester), the xe2x80x9ctwo stepsxe2x80x9d are actually identical and are therefore, in reality, only one step. In fact, Emmons indicates that the xe2x80x9ctwo stepsxe2x80x9d may occur concurrently or simultaneously.
Several problems exist in the prior art that are addressed by the present invention. More specifically, the prior art processes generate polymers having random placement of monomer residues and have less flexibility in polyamide structure design and property optimization. Still further, the polymers made according to the prior art have low molecular weights, which results in sub-optimal levels of wet strength.
The present invention contemplates polyamide pre-polymers, polyamide polymers, a multi-step process for the synthesis of polyamide pre-polymers and polyamide polymers using acrylates and at least one monomer containing at least two primary amines (hereinafter referred to as xe2x80x9cdiaminexe2x80x9d), and resins resulting from reacting a polyamide polymer of the present invention with an epihalohydrin.
The present invention relates to a process comprising the steps of: (a) the Michael addition of a first diamine to an acrylate, thereby forming a reaction mixture containing an amine-containing diester or diacid intermediate pre-polymer reaction product; and (b) carrying out aminolysis and polymerization using either of two methods, Method (b1) or Method (b2). Method (b1) comprises adding a second diamine to the reaction mixture and heating the reaction mixture to an elevated temperature for a period of time ranging from about 2 hours to about 8 hours. Method (b2) adds a second diamine to the reaction mixture and introduces an enzyme, acting as a catalyst, into the reaction mixture, which is then heated to an elevated temperature. Preferably, the enzyme introduced into Method (b2) in the polymerization reaction is a hydrolase enzyme, wherein about 0.1% to about 10% by weight of the enzyme, relative to the total weight of the monomers (diamine and acrylate), is used. The final reaction product resulting from a process of the present invention may be either a linear or a branched condensation polymer having a molecular weight ranging from about 1490 to about 200,000 daltons and a polydispersity (Mw/Mn) ranging from about 2.0 to about 10.0.
A method for making a polyamide resin comprising the steps of (i) reacting the final reaction product, a polyamide polymer, with an epihalohydrin, and (ii) allowing the reaction to proceed where the final reaction product is cross-linked with itself.
An object of the present invention is to synthesize and develop regio-regular polyamide structures that contain a high proportion of secondary amine groups to carbons on the polymer repeat units, and have a high molecular weight, as well as provide a process for the synthesis of those polyamide polymers, polyamide pre-polymers, and ultimately resins that were reacted with a halohydrin.
The present invention contemplates polyamide pre-polymers, polyamide polymers, a multi-step process for the synthesis of polyamide polymers as well as polyamide pre-polymers using acrylates and at least one monomer containing at least two primary amines, and resins resulting from reacting a polyamide polymer of the present invention with an epihalohydrin.
There are several distinct advantages conferred by the present invention. First, the development of a multi-step process allows for the production of more general polyamide structures than is currently found in the art, thereby providing greater flexibility in structure design and property optimization such that there is a wider range of possible polymer structures. Second, the optional use of different diamines in steps (a) and (b) further provides for greater flexibility in polyamide structure design and property optimization. However, even when the same diamine is used in both reaction steps (a) and (b), the present invention differs from the prior art. For example, according to the prior art, when the diamine is NH2xe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)xxe2x80x94NH2 and R is a C2-C6 alkylene moiety, the polymer repeat unit is:
[NHxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)xxe2x80x94NHxe2x80x94COxe2x80x94Rxe2x80x94]
where 0xe2x89xa6xxe2x89xa66, and 2xe2x89xa6nxe2x89xa610. For easier visualization, W has been denoted as [NHxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)xxe2x80x94NH]. Thus the same repeat unit is:
[Wxe2x80x94COxe2x80x94Rxe2x80x94]
However, when the process of the present invention utilizes the above-noted starting materials, a different polymer repeat sequence is obtained, for example:
[Wxe2x80x94COxe2x80x94Rxe2x80x94Wxe2x80x94Rxe2x80x94CO]
A third advantage of the present invention is that typical polymers in the art are generated having a random placement of monomer residues, whereas the process of the present invention generates polyamide polymers having discrete and regio-regular polymer structures. These regio-regular and discrete polymers are advantageous because they allow structures to be designed with greater specificity, and therefore, increase the likelihood of greater numbers of the polymers having a particular functionality. The fourth advantage of the present invention is that the polyamide polymers synthesized according to typical methods known in the art (e.g., Emmons) have low molecular weights (about 300 to 1000 Daltons) whereas the polyamide polymers of the present invention have higher molecular weights (at least 1490 Daltons, but usually much higher), which provide improved wet strength.
Note that in comparison to conventional adipic acid-DETA polymers (e.g., Espy, 1995), the present invention provides polyamide polymers having at least one additional secondary amine per repeating unit when using the same diamine as the starting materials thereby enabling the polymer to react with an epihalohydrin and allowing for crosslinking of the polymer. The polyamide pre-polymers according to the present invention, such as those made using methyl acrylate and diethylene triamine (DETA) or dipropylene triamine (DPTA), have one secondary amine for about every 3-5 carbons, whereas in the backbone of a conventional adipate/DETA pre-polymer, synthesized by the polymerization of adipic acid and DETA, there is only 1 secondary amine for every 10 carbons on the polymer repeat units. The level of functionality on the backbone of a resin is, to some extent, determinative of the efficiency of the resin as a wet strength agent, and since the self-crosslinking and reactions with the pulp fiber each contribute to wet strength properties, a higher proportion of these functionalities on a resin may produce a more efficient resin because there is a high proportion of free secondary amines in the polymer backbone that can react with an epihalohydrin to afford high levels of azetidinium and/or epoxide functionalities. Thus, it is desirable to have a higher proportion of the secondary amine on the backbone of a polyamide pre-polymer because this proportion relates to the end-use properties of the resin.
The term xe2x80x9cregio-regularxe2x80x9d, as used herein, refers to the well-defined repeat placement of the monomer residues to form a polymer structure. It is in contradistinction to xe2x80x9crandomxe2x80x9d placement, which denotes the co-existence of various compositions and/or structures.
The present invention contemplates a synthesis process having at least two chemically distinct steps for the synthesis of polyamide pre-polymers and polyamide polymers wherein the process comprises the steps of: (a) adding a first diamine to an acrylate thereby forming a reaction mixture, wherein the diamine and acrylate are in a ratio of approximately 1:2 respectively, and resulting in an amine-containing diester or diacid intermediate pre-polymer reaction product; and (b) adding a second diamine to the reaction product of step (a) and allowing the polymerization to proceed to completion, thereby forming a final reaction product. Steps (a) and (b) may be performed separately or in situ, with or without the purification of the diester or diacid intermediate reaction pre-polymer. The synthesis process is typically performed neat, however, it may also utilize an organic solvent or aqueous solution comprising up to about 30% water.
Step (a) is the Michael addition of a first diamine to an acrylate to form an amine-containing diester or diacid, wherein the mole ratio is about 1:2, respectively.
Further, the sequence of the addition of the first diamine to the acrylate and the stoichiometry of these reactants is critical. Preferably, the Michael addition (Step (a)) is performed by gradually adding, over about 20-60 minutes, 2 moles of an acrylate to 1 mole of a first diamine at room temperature, for example about 20xc2x0 C. to about 30xc2x0 C., in the absence of a solvent, or in the presence of either alcohol or water. The addition of water to the reaction mixture enhances the rate of the Michael addition. However, in step (a), the concurrent addition of the acrylate and the first diamine is acceptable, and in fact preferred, when a water-containing diamine is used during the Michael addition reaction.
In a general and representative sense, the resultant product of step (a) is an intermediate pre-polymer reaction product, also contemplated by the present invention, having the formula:
R1OCOCHR2CH2xe2x80x94NH[(CH2)nX(CH2)nNH]mxe2x80x94CH2CH2R2COOR1 
wherein R1 is selected from the group consisting of substituted C1-C6 alkyl group, unsubstituted C1-C6 alkyl group, and hydrogen; R2 is selected from the group consisting of H and C1-C2 alkyl group; X is selected from the group consisting of O, NH, S, CH3Nxe2x80x94, alkyl (C1-C6) and aryl; n ranges from 1-10; and m ranges from 1-6. More preferably, R1 is a methyl group and R2 is hydrogen.
For example, the reaction of DETA and methyl acrylate gives the following product:
NH2CH2CH2NHCH2CH2NH2+CH2=CHxe2x80x94COOCH3xe2x86x92CH3OCOxe2x80x94CH2CH2xe2x80x94NHCH2CH2NHCH2CH2NHxe2x80x94CH2CH2COOCH3 
Step (a) is an exothermic reaction, and therefore, the reaction vessel should be cooled through any suitable means known in the art. Preferably, the reaction temperature for Step (a) is in the range of about 10xc2x0 C. to about 60xc2x0 C., more preferably about 15xc2x0 C. to about 40xc2x0 C., and most preferably about 20xc2x0 C. to about 30xc2x0 C.
Step (b) of the present invention, comprising aminolysis and polymerization, may be carried out using either of two methods, Method (b1) or Method (b2). In Methods (b1) and (b2), the second diamine may be either the same diamine or a different diamine than was used in Step (a). For example, the reaction of the DETA-acrylate diester with N-methyl-bis(aminopropyl)amine (MBAPA) would give the following product:
CH3OCOxe2x80x94CH2CH2xe2x80x94NHCH2CH2NHCH2CH2NHxe2x80x94CH2CH2COOCH3 
+NH2CH2CH2CH2N(CH3)CH2CH2CH2NH2xe2x86x92
[COCH2CH2xe2x80x94NHCH2CH2NHCH2CH2NHxe2x80x94CH2CH2COxe2x80x94NHCH2CH2CH2N(CH3)CH2CH2CH2NH]
Method (b1) comprises adding a second diamine, in approximately the same molar amount as the first diamine used in step (a), to the reaction mixture of step (a) and heating this reaction mixture to an elevated temperature in the range of about 70xc2x0 C. to about 140xc2x0 C., preferably to a temperature of about 130xc2x0 C., for a period of time ranging from about 2 hours to about 8 hours. This reaction time is partially determinative of the molecular weight of the final reaction product, wherein a longer reaction time generally corresponds to a higher molecular weight. The reaction time can be adjusted to provide a final reaction product having the appropriate molecular weight for the desired application. The progress of polymerization can be assessed monitoring the viscosity increase of the aqueous solution. Typically, at the beginning of the reaction, the product has no viscosity at all, but as the polymerization reaction proceeds, the viscosity increases. A sample can be withdrawn from the reaction mixture, wherein the viscosity of the aqueous solution can be determined, such that the higher the viscosity, the higher the molecular weight of the polyamide that was produced.
Method (b2) comprises adding a second diamine, in approximately the same molar amount as the first diamine used in step (a), to the reaction mixture of step (a) and introducing an enzyme, acting as a catalyst, into the reaction mixture which is then heated to an elevated temperature ranging from about 60xc2x0 C. to about 80xc2x0 C. for a period of time ranging from about 2 hours to about 16 hours. Preferably, the enzyme introduced into Method (b2) in the polymerization reaction is a hydrolase enzyme, more preferably any lipase or protease selected from the group consisting of plants, bacteria, fungi and yeast. Still more preferably, the enzyme is a lipase selected from the group consisting of yeast Candida antarctica and Mucor miehei, most preferably the lipase is yeast Candida antarctica. Preferably, about 0.1% to about 10% by weight of the enzyme, relative to the total weight of the monomers (diamine and alkyl acrylate), is used. More preferably, about 0.5% to about 5%, and most preferably about 1% to about 3% by weight of the enzyme, relative to the total weight of the monomers (diamine and acrylate), is used. The enzyme functions as a catalyst to activate the carbonyl group of the diester or diacid and to facilitate the nucleophilic attack by the amino group of the diamine, thereby enhancing the reaction rate of polyamide condensation. Generally, the amount of enzyme introduced into the reaction mixture corresponds to the desired molecular weight of the polymer, wherein a low amount of enzyme results in a slow reaction, thereby producing a low molecular weight polymer. Conversely, a higher amount of enzyme introduced into the reaction mixture results in a polymer having a higher molecular weight. For example, in the preferred embodiment, use of about 1% by weight of the enzyme, relative to the total weight of the monomers (diamine and acrylate) may correlate to a molecular weight in the range of about 2000-4000, whereas use of about 3% by weight of the enzyme, relative to the total weight of the monomers (diamine and acrylate) may correlate to a molecular weight of about 7000 to 240,000.
Examples of suitable acrylates contemplated by this invention include, but are not limited to, alkyl acrylates, alkyl methacrylates, aryl acrylate, aryl methacrylates, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, phenyl, and benzyl esters of acrylic acid, methacrylic acid, ethacrylic acid, and butacrylic acid and combinations thereof. The preferred acrylates are methyl acrylate (MA), ethyl acrylate, methyl methacrylate (MMA), and ethyl methacrylate and combinations thereof. The most preferred acrylates are methyl acrylate (MA) and methyl methacrylate (MMA) and combinations thereof.
Examples of suitable diamines contemplated by the present invention include, but are not limited to, diethylene triamine (DETA) or its analogs, N-(3-aminopropyl)-1,3-propanediamine (dipropylene triamine or DPTA), ethylene diamine (EDA), 1,6-hexamethylenediamine (HMDA), triethylene tetraamine (TETA), tetraethylene pentaamine (TEPA), N-methyl-bis(aminopropyl)amine (MBAPA), bis(hexamethylene triamine) (BHMT), tripropylene tetraamine, tetrapropylene pentaamine, spermine, spermidine, 1-phenyl-2,4-pentane diamine, 2-phenyl-1,3-propanediamine, 2-methyl-1,5-pentane diamine, and phenylene diamine and combinations thereof. The preferred diamines are diethylene triamine (DETA), dipropylene triamine (DPTA), 1,6-hexamethylenediamine (HMDA), triethylene tetraamine (TETA), N-methyl-bis(aminopropyl)amine (MBAPA), and bis(hexamethylene triamine) (BHMT) and combinations thereof. The most preferred diamines are diethylene triamine (DETA), dipropylene triamine (DPTA), 1,6-hexamethylenediamine (HMDA), and N-methyl-bis(aminopropyl)amine (MBAPA) and combinations thereof.
The final reaction product, a polyamide polymer also contemplated by the present invention, resulting from steps (a) and (b) has the formula:
[xe2x80x94COCHR2CH2NH[(CH2)nX(CH2)nNH]mCH2CHR2CONH[(CH2)nxe2x80x2Y(CH2)nxe2x80x2NH]mxe2x80x2]p 
wherein R2 is selected from the group consisting of H and C1-C2 alkyl group; X is selected from the group consisting of O, NH, S, CH3Nxe2x80x94, alkyl (C1-C6) and aryl; Y is selected from the group consisting of O, NH, S, CH3Nxe2x80x94, alkyl (C1-C6) and aryl; n and nxe2x80x2 range from 1-10; m and mxe2x80x2 range from 1-6; and p ranges from 1-1000. Preferably, R2 is selected from the group consisting of H and methyl; X is selected from the group consisting of NH and CH3Nxe2x80x94; Y is selected from the group consisting of NH and CH3N; n and nxe2x80x2 range from 2-3; m and mxe2x80x2 are 1; and p ranges from 10-100. More preferably, R2 is H; X is NH; Y is NH; n and nxe2x80x2 range from 2-3; m and mxe2x80x2 are 1; and p ranges from 20-100.
The final reaction product may be either a linear or a branched condensation polymer having a molecular weight ranging from about 1490 to about 200,000 daltons and a polydispersity (Mw/Mn) ranging from about 2.0 to about 10.0. For example, the linear polymer structure from the reaction product of DETA-acrylate diester and MBAPA would be:
[COCH2CH2xe2x80x94NHCH2CH2NHCH2CH2NHxe2x80x94CH2CH2COxe2x80x94NHCH2CH2CH2N(CH3)CH2CH2CH2NH]
One of the possible branch structures from the same reaction is given as follows: 
The molecular weight of the final reaction product varies according to the reaction temperature, the specific monomers used for the reaction, the reaction time and the amount of enzyme incorporated into the reaction mixture depending on the particular method utilized in the inventive process. A typical functional polymer of the present invention resulting from the above-described process has an average number molecular weight (Mn) of about 3,500 daltons, a molecular weight (Mw) ranging from about 9,000 to about 14,000 daltons, a polydispersity (Mw/Mn) ranging from about 3 to about 6 and is generally a semi-solid material having a light color.
The present invention further contemplates reacting the final reaction product with an epihalohydrin, preferably epichlorohydrin, thereby resulting in a polyamide resin, wherein the polymer has the ability to cross-link with itself or to react with other materials, such as paper, pulp, wool, wood and the like. A method for making a polyamide resin comprises the steps of (i) reacting the final reaction product, a polyamide polymer, with an epihalohydrin, and (ii) allowing the reaction to proceed where the final reaction product is cross-linked with itself. When the polymers of the present invention are treated with epichlorohydrin under the appropriate reaction conditions (i.e., those conditions shown in Examples 8 and 9 are preferred), the resulting resins are water-soluble, cationic resins. Manipulation of temperatures aid in determining the functionality of the resin, for example, in reacting the final reaction product with an epihalohydrin, it may occur at a temperature up to 70xc2x0 C., wherein the temperature may remain constant throughout the reaction or it may be multi-staged such that a low temperature is used initially and subsequently utilizes an elevated temperature. Furthermore the pH of this reaction must be basic, wherein the initial pH may be 9.0 or higher, in order to have the non-protonated 2nd amines available to the alkylation reaction. Nevertheless, no pH control is necessary during the reaction since the polyamide solution is initially alkaline. After the reaction, the pH has to be further brought down to acidic conditions using H2SO4 or HCl to a pH of about 6. These types of resins may be used as wet strength resins and/or creping aids in papermaking processes. The polyamide resin according to the present invention comprises the formula:
[xe2x80x94COCHR2CH2K[(CH2)nX(CH2)nK]mCH2CHR2CONH[(CH2)nxe2x80x2Y(CH2)nxe2x80x2NH]mxe2x80x2]p 
wherein R2 is selected from the group consisting of H and C1-C2 alkyl group; n and nxe2x80x2 range from 1-10; m and mxe2x80x2 range from 1-6; p ranges from 1-1000; K is selected from the group consisting of 
X is selected from the group consisting of O, K, S, Q, alkyl (C1-C6) and aryl; Y is selected from the group consisting of O, K, S, Q, alkyl (C1-C6) and aryl; and Q is selected from the group consisting of 
The present invention further contemplates cellulosic products produced using a resin of the present invention in any conventional process typically utilized to produce cellulosic products such as paper towels, napkins, writing paper, and the like.
The embodiments of the present invention are further defined in the following Examples. It should be understood that these Examples are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various uses and conditions. Thus various modifications of the present invention in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing description. Although the invention has been described with reference to particular means, materials and embodiments, it is to be understood that the invention is not limited to the particulars disclosed, and extends to all equivalents within the scope of the claims.